Producing frequency-modulated sonar systems for commercial applications such as fish finding routinely faces cost pressures. Thus, advanced signal processing techniques must be implemented in an efficient, cost-effective manner. For example, it is desirable to offer relatively high power (such as 1 kW) over a wideband frequency range such as 25 kHz to 255 kHz. However, the cost pressures for commercial implementations prevent the use of convenient solutions such as a linear power amplifier.
In a conventional sonar, the power amplifier drives a transducer through a transformer. The transformer isolates the transducer and also functions to impedance match the transducer to the amplifier. In general, such a transformer should have a relatively low insertion loss to maximize the power delivered to the transducer and also to minimize the associated heating effects from the insertion loss. But maintaining a low insertion loss is problematic in view of real-world effects such as coupling between transformer windings and associated parasitics.
The demands on transformer performance are exacerbated in a wideband sonar application. Such wideband performance is desirable in that shallow water performance favors a relatively high frequency sonar pulse whereas deeper water performance is enhanced with a relatively lower frequency sonar pulse. The transformer must perform at both the relatively low frequencies as well as the relatively high frequencies and thus requires suitable wideband performance. Achieving a desired performance for an isolating transformer in a wideband sonar system is difficult in light of the increased reactance encountered when operating transducers over a wide bandwidth. Wideband isolating transformers must satisfy conflicting demands in that low frequency operation demands high shunt inductance whereas suitable high frequency operation requires low inductance (in particular, low leakage inductance) to avoid resonating with the capacitive load presented by the transducer.
Accordingly, there is a need in the art for improved sonar systems that offer frequency agile performance and relatively high power at low cost. In addition, there is a need in the art for isolating transformers that satisfy the conflicting demands presented by wideband sonar applications.